Mitochondrially localized MPZL3 emerges as a signaling hub of mammalian physiology.

MPZL3 is a nuclear-encoded, mitochondrially localized, immunoglobulin-like V-type protein that functions as a key regulator of epithelial cell differentiation, lipid metabolism, ROS production, glycemic control, and energy expenditure. Recently, MPZL3 has surfaced as an important modulator of sebaceous gland function and of hair follicle cycling, an organ transformation process that is also governed by peripheral clock gene activity and PPARγ. Given the phenotype similarities and differences between Mpzl3 and Pparγ knockout mice, we propose that MPZL3 serves as a signaling hub that is regulated by core clock gene products and/or PPARγ to translate signals from these nuclear transcription factors to the mitochondria to modulate circadian and metabolic regulation. Conservation between murine and human MPZL3 suggests that human MPZL3 may have similarly complex functions in health and disease. We summarize current knowledge and discuss future directions to elucidate the full spectrum of MPZL3 functions in mammalian physiology.

PAM haploinsufficiency does not accelerate the development of diet- and human IAPP-induced diabetes in mice.

AIMS/HYPOTHESIS: Peptide hormones are first synthesised as larger, inactive precursors that are converted to their active forms by endopeptidase cleavage and post-translational modifications, such as amidation. Recent, large-scale genome-wide studies have suggested that two coding variants of the amidating enzyme, peptidylglycine α-amidating monooxygenase (PAM), are associated with impaired insulin secretion and increased type 2 diabetes risk. We aimed to elucidate the role of PAM in modulating beta cell peptide amidation, beta cell function and the development of diabetes. METHODS: PAM transcript and protein levels were analysed in mouse islets following induction of endoplasmic reticulum (ER) or cytokine stress, and PAM expression patterns were examined in human islets. To study whether haploinsufficiency of PAM accelerates the development of diabetes, Pam+/- and Pam+/+ mice were fed a low-fat diet (LFD) or high-fat diet (HFD) and glucose homeostasis was assessed. Since aggregates of the PAM substrate human islet amyloid polypeptide (hIAPP) lead to islet inflammation and beta cell failure, we also investigated whether PAM haploinsufficiency accelerated hIAPP-induced diabetes and islet amyloid formation in Pam+/- and Pam+/+ mice with beta cell expression of hIAPP. RESULTS: Immunostaining revealed high expression of PAM in alpha, beta and delta cells in human pancreatic islets. Pam mRNA and PAM protein expression were reduced in mouse islets following administration of an HFD, and in isolated islets following induction of ER stress with thapsigargin, or cytokine stress with IL-1ß, IFN-γ and TFN-α. Despite Pam+/- only having 50% PAM expression and enzyme activity as compared with Pam+/+ mice, glucose tolerance and body mass composition were comparable in the two models. After 24 weeks of HFD, both Pam+/- and Pam+/+ mice had insulin resistance and impaired glucose tolerance, but no differences in glucose tolerance, insulin sensitivity or plasma insulin levels were observed in PAM haploinsufficient mice. Islet amyloid formation and beta cell function were also similar in Pam+/- and Pam+/+ mice with beta cell expression of hIAPP. CONCLUSIONS/INTERPRETATION: Haploinsufficiency of PAM in mice does not accelerate the development of diet-induced obesity or hIAPP transgene-induced diabetes.

Correction to: PAM haploinsufficiency does not accelerate the development of diet and human IAPP-induced diabetes in mice.

Unfortunately, the human islet checklist was omitted from the electronic supplementary material (ESM) linked to this paper.

Deficiency of the RIIß subunit of PKA affects locomotor activity and energy homeostasis in distinct neuronal populations.

Targeted disruption of RIIß-protein kinase A (PKA) in mice leads to a lean phenotype, increased nocturnal locomotor activity, and activation of brown adipose tissue. Because RIIß is abundantly expressed in both white and brown adipose tissue as well as the brain, the contribution of neuronal vs. peripheral PKA to these phenotypes was investigated. We used a Cre-Lox strategy to reexpress RIIß in a tissue-specific manner in either adipocytes or neurons. Mice with adipocyte-specific RIIß reexpression remained hyperactive and lean, but pan-neuronal RIIß reexpression reversed both phenotypes. Selective RIIß reexpression in all striatal medium spiny neurons with Darpp32-Cre corrected the hyperlocomotor phenotype, but the mice remained lean. Further analysis revealed that RIIß reexpression in D2 dopamine receptor-expressing medium spiny neurons corrected the hyperlocomotor phenotype, which demonstrated that the lean phenotype in RIIß-PKA-deficient mice does not develop because of increased locomotor activity. To identify the neurons responsible for the lean phenotype, we used specific Cre-driver mice to reexpress RIIß in agouti-related peptide (AgRP)-, proopiomelanocortin (POMC)-, single-minded 1 (Sim1)-, or steroidogenic factor 1 (SF1)-expressing neurons in the hypothalamus, but observed no rescue of the lean phenotype. However, when RIIß was reexpressed in multiple regions of the hypothalamus and striatum driven by Rip2-Cre, or specifically in GABAergic neurons driven by Vgat-ires-Cre, both the hyperactive and lean phenotypes were completely corrected. Bilateral injection of adeno-associated virus1 (AAV1)-Cre directly into the hypothalamus caused reexpression of RIIß and partially reversed the lean phenotype. These data demonstrate that RIIß-PKA deficiency in a subset of hypothalamic GABAergic neurons leads to the lean phenotype.

Mutation of putative GRK phosphorylation sites in the cannabinoid receptor 1 (CB1R) confers resistance to cannabinoid tolerance and hypersensitivity to cannabinoids in mice.

For many G-protein-coupled receptors (GPCRs), including cannabinoid receptor 1 (CB1R), desensitization has been proposed as a principal mechanism driving initial tolerance to agonists. GPCR desensitization typically requires phosphorylation by a G-protein-coupled receptor kinase (GRK) and interaction of the phosphorylated receptor with an arrestin. In simple model systems, CB1R is desensitized by GRK phosphorylation at two serine residues (S426 and S430). However, the role of these serine residues in tolerance and dependence for cannabinoids in vivo was unclear. Therefore, we generated mice where S426 and S430 were mutated to nonphosphorylatable alanines (S426A/S430A). S426A/S430A mutant mice were more sensitive to acutely administered delta-9-tetrahydrocannabinol (Δ(9)-THC), have delayed tolerance to Δ(9)-THC, and showed increased dependence for Δ(9)-THC. S426A/S430A mutants also showed increased responses to elevated levels of endogenous cannabinoids. CB1R desensitization in the periaqueductal gray and spinal cord following 7 d of treatment with Δ(9)-THC was absent in S426A/S430A mutants. Δ(9)-THC-induced downregulation of CB1R in the spinal cord was also absent in S426A/S430A mutants. Cultured autaptic hippocampal neurons from S426A/S430A mice showed enhanced endocannabinoid-mediated depolarization-induced suppression of excitation (DSE) and reduced agonist-mediated desensitization of DSE. These results indicate that S426 and S430 play major roles in the acute response to, tolerance to, and dependence on cannabinoids. Additionally, S426A/S430A mice are a novel model for studying pathophysiological processes thought to involve excessive endocannabinoid signaling such as drug addiction and metabolic disease. These mice also validate the approach of mutating GRK phosphorylation sites involved in desensitization as a general means to confer exaggerated signaling to GPCRs in vivo.

Genetic ablation of myelin protein zero-like 3 in mice increases energy expenditure, improves glycemic control, and reduces hepatic lipid synthesis.

Obesity continues to be a global health problem, and thus it is imperative that new pathways regulating energy balance be identified. Recently, it was reported: (Hayashi K, Cao T, Passmore H, Jourdan-Le Saux C, Fogelgren B, Khan S, Hornstra I, Kim Y, Hayashi M, Csiszar K. J Invest Dermatol 123: 864-871, 2004) that mice carrying a missense mutation in myelin protein zero-like 3 (Mpzl3rc) have reduced body weight. To determine how Mpzl3 controls energy balance in vivo, we generated mice deficient in myelin protein zero-like 3 (Mpzl3-KO). Interestingly, KO mice were hyperphagic yet had reduced body weight and fat mass. Moreover, KO mice were highly resistant to body weight and fat mass gain after exposure to a high-fat, energy-dense diet. These effects on body weight and adiposity were driven, in part, by a pronounced increase in whole body energy expenditure levels in KO mice. KO mice also had reduced blood glucose levels during an intraperitoneal glucose challenge and significant reductions in circulating insulin levels suggesting an increase in insulin sensitivity. In addition, there was an overall increase in oxidative capacity and contractile force in skeletal muscle isolated from KO mice. Hepatic triglyceride levels were reduced by 92% in livers of KO mice, in part due to a reduction in de novo lipid synthesis. Interestingly, Mpzl3 mRNA expression in liver was increased in diet-induced obese mice. Moreover, KO mice exhibited an increase in insulin-stimulated Akt signaling in the liver, further demonstrating that Mpzl3 can regulate insulin sensitivity in this tissue. We have determined that Mpzl3 has a novel physiological role in controlling body weight regulation, energy expenditure, glycemic control, and hepatic triglyceride synthesis in mice.

Mice lacking δ-opioid receptors resist the development of diet-induced obesity.

Pharmacological manipulation of opioid receptors alters feeding behavior. However, the individual contributions of each opioid receptor subtype on energy balance remain largely unknown. Herein, we investigated whether genetic disruption of the δ-opioid receptor (DOR) also controls energy homeostasis. Mice lacking DOR and wild-type mice were fed with standard diet and high-energy diet (HED). Mice were analyzed in vivo with the indirect calorimetry system, and tissues were analyzed by real-time PCR and Western blot analysis. DOR-knockout (KO) mice gained less weight (P<0.01) and had lower fat mass (P<0.01) when compared to WT mice fed an HED. Although DOR-KO mice were hyperphagic, they showed higher energy expenditure (P<0.05), which was the result of an increased activation of the thermogenic program in brown adipose tissue. The increased nonshivering thermogenesis involved the stimulation of uncoupling protein 1 (UCP1; P<0.01), peroxisome proliferator-activated receptor γ coactivator (PGC1α; P<0.05), and fibroblast growth factor 21 (FGF21; P<0.01). DOR deficiency also led to an attenuation of triglyceride content in the liver (P<0.05) in response to an HED. These findings reveal a novel role of DOR in the control of thermogenic markers and energy expenditure, and they provide a potential new therapeutic approach for the treatment of obesity.

kappa-Opioid receptors control the metabolic response to a high-energy diet in mice.

General opioid receptor antagonists reduce food intake and body weight in rodents, but the contributions of specific receptor subtypes are unknown. We examined whether genetic deletion of the kappa-opioid receptor (KOR) in mice alters metabolic physiology. KOR-knockout (KO) and wild-type (WT) mice were fed a high-energy diet (HED) for 16 wk. KO mice had 28% lower body weight and 45% lower fat mass when compared to WT mice fed an HED. No differences in caloric intake were found. An HED reduced energy expenditure in WT mice, but not in KO mice. KOR deficiency led to an attenuation of triglyceride synthesis in the liver. Malonyl CoA levels were also reduced in response to an HED, thereby promoting hepatic beta-oxidation. Glycemic control was also found to be improved in KO mice. These data suggest a key role for KORs in the central nervous system regulation of the metabolic adaptation to an HED, as we were unable to detect expression of KOR in liver, white adipose tissue, or skeletal muscle in WT mice. This study provides the first evidence that KORs play an essential physiological role in the control of hepatic lipid metabolism, and KOR activation is a permissive signal toward fat storage.-Czyzyk, T. A., Nogueiras, R., Lockwood, J. F., McKinzie, J. H., Coskun, T., Pintar, J. E., Hammond, C., Tschöp, M. H., Statnick, M. A. kappa-Opioid receptors control the metabolic response to a high-energy diet in mice.

Disruption of the RIIbeta subunit of PKA reverses the obesity syndrome of Agouti lethal yellow mice.

Agouti lethal yellow (A(y)) mice express agouti ectopically because of a genetic rearrangement at the agouti locus. The agouti peptide is a potent antagonist of the melanocortin 4 receptor (MC4R) expressed in neurons, and this leads to hyperphagia, hypoactivity, and increased fat mass. The MC4R signals through Gs and is thought to stimulate the production of cAMP and activation of downstream cAMP effector molecules such as PKA. Disruption of the RIIbeta regulatory subunit gene of PKA results in release of the active catalytic subunit and an increase in basal PKA activity in cells where RIIbeta is highly expressed. Because RIIbeta is expressed in neurons including those in the hypothalamic nuclei where MC4R is prominent we tested the possibility that the RIIbeta knockout might rescue the body weight phenotypes of the A(y) mice. Disruption of the RIIbeta PKA regulatory subunit gene in mice leads to a 50% reduction in white adipose tissue and resistance to diet-induced obesity and hyperglycemia. The RIIbeta mutation rescued the elevated body weight, hyperphagia, and obesity of A(y) mice. Partial rescue of the A(y) phenotypes was even observed on an RIIbeta heterozygote background. These results suggest that the RIIbeta gene mutation alters adiposity and locomotor activity by modifying PKA signaling pathways downstream of the agouti antagonism of MC4R in the hypothalamus.

Antisense oligonucleotide-mediated knockdown of Mpzl3 attenuates the negative metabolic effects of diet-induced obesity in mice.

Previously, we demonstrated that global knockout (KO) of the gene encoding myelin protein zero-like 3 (Mpzl3) results in reduced body weight and adiposity, increased energy expenditure, and reduced hepatic lipid synthesis in mice. These mice also exhibit cyclic and progressive alopecia which may contribute to the observed hypermetabolic phenotype. The goal of the current study was to determine if acute and peripherally restricted knockdown of Mpzl3 could ameliorate the negative metabolic effects of exposure to a high-fat and sucrose, energy-dense (HED) diet similar to what was observed in global Mpzl3 KO mice in the absence of a skin phenotype. Mpzl3 antisense oligonucleotide (ASO) administration dose-dependently decreased fat mass and circulating lipids in HED-fed C57BL/6N mice. These changes were accompanied by a decrease in respiratory exchange ratio, a reduction in energy expenditure and food intake, a decrease in expression of genes regulating de novo lipogenesis in white adipose tissue, and an upregulation of genes associated with steroid hormone biosynthesis in liver, thermogenesis in brown adipose tissue and fatty acid transport in skeletal muscle. These data demonstrate that resistance to the negative metabolic effects of HED is a direct effect of Mpzl3 knockdown, rather than compensatory changes that could be associated with deletion of Mpzl3 during development in global KO mice. Inhibiting MPZL3 could be a potential therapeutic approach for the treatment of obesity and associated dyslipidemia.

The propeptide precursor proSAAS is involved in fetal neuropeptide processing and body weight regulation.

Mice with a targeted mutation in proSAAS have been generated to investigate whether peptides derived from this precursor could function as an inhibitor of prohormone convertase 1/3 (PC1/3) in vivo as well as to determine any alternate roles for proSAAS in nervous and endocrine tissues. Fetal mice lacking proSAAS exhibit complete, adult-like processing of prodynorphin in the prenatal brain instead of the incomplete processing seen in the brains of wild-type fetal mice where inhibitory proSAAS intermediates are transiently accumulated. This study provides evidence that proSAAS is directly involved in the prenatal regulation of neuropeptide processing in vivo. However, adult mice lacking proSAAS have normal levels of all peptides detected using a peptidomics approach, suggesting that PC1/3 activity is not affected by the absence of proSAAS in adult mice. ProSAAS knockout mice exhibit decreased locomotion and a male-specific 10-15% decrease in body weight, but maintain normal fasting blood glucose levels and are able to efficiently clear glucose from the blood in response to a glucose challenge. This work suggests that proSAAS-derived peptides can inhibit PC1/3 in embryonic brain, but in the adult brain proSAAS peptides may function as neuropeptides that regulate body weight and potentially other behaviors.

Interactions of peptide amidation and copper: novel biomarkers and mechanisms of neural dysfunction.

Mammalian genomes encode only a small number of cuproenzymes. The many genes involved in coordinating copper uptake, distribution, storage and efflux make gene/nutrient interactions especially important for these cuproenzymes. Copper deficiency and copper excess both disrupt neural function. Using mice heterozygous for peptidylglycine alpha-amidating monooxygenase (PAM), a cuproenzyme essential for the synthesis of many neuropeptides, we identified alterations in anxiety-like behavior, thermoregulation and seizure sensitivity. Dietary copper supplementation reversed a subset of these deficits. Wildtype mice maintained on a marginally copper-deficient diet exhibited some of the same deficits observed in PAM(+/-) mice and displayed alterations in PAM metabolism. Altered copper homeostasis in PAM(+/-) mice suggested a role for PAM in the cell type specific regulation of copper metabolism. Physiological functions sensitive to genetic limitations of PAM that are reversed by supplemental copper and mimicked by copper deficiency may serve as indicators of marginal copper deficiency.

Alterations in nociception and morphine antinociception in mice fed a high-fat diet.

Currently, more than 78.6 million adults in the United States are obese. A majority of the patient population receiving treatment for pain symptoms is derived from this subpopulation. Environmental factors, including the increased availability of food high in fat and sugar, contribute to the continued rise in the rates of obesity. The focus of this study was to investigate whether long-term exposure to a high-fat, energy-dense diet enhances baseline thermal and inflammatory nociception while reducing sensitivity to morphine-induced antinociception. Antinociceptive and hypothermic responses to morphine were determined in male and female C57BL/6N mice fed either a "western-style" diet high in fat and sucrose (HED) or a standard low-fat chow diet for 15 weeks. Antinociception was assessed using both the hot plate and tail flick tests of acute thermal pain and the formalin test of inflammatory pain. Acute administration of morphine dose-dependently increased antinociception in the hot plate and tail flick assays for mice of both sexes fed chow and HED. However, female mice displayed lower antinociceptive response to morphine compared to males in the tail-flick test. Hypothermic responses to acute morphine were also assessed in mice fed chow or HED. Male and female mice fed chow, and female mice fed HED displayed similar hypothermic responses to morphine. However, males fed HED did not exhibit morphine-induced hypothermia. Tolerance to the antinociceptive and hypothermic effects of morphine was assessed after ten days of repeated daily administration (10mg/kg morphine). Male mice fed chow or HED developed tolerance to morphine in the hot plate test. However, females fed HED did not. In the tail flick assay, only mice fed HED developed tolerance to morphine. All groups showed tolerance to morphine-induced hypothermia. In the formalin test, we found that both male and female mice fed HED had reduced sensitivity to the antinociceptive effects of morphine (6mg/kg). Collectively, these data suggest that sensitivity and tolerance to the antinociceptive effects of morphine may be dependent on diet and sex in the hot plate and tail flick thermal pain models, and that the acute antinociceptive effects of morphine in the formalin inflammatory pain model may also be dependent on these two factors. In addition, diet and sex can influence morphine-induced hypothermia. Exposure to an HED may lead to changes in neuronal signaling pathways that alter nociceptive responses to noxious stimuli in a sex-specific manner. Thus, dietary modifications might be a useful way to impact pain therapy.

Endogenous kappa-opioid receptor systems regulate mesoaccumbal dopamine dynamics and vulnerability to cocaine.

Genetic and pharmacological approaches were used to examine kappa-opioid receptor (KOR-1) regulation of dopamine (DA) dynamics in the nucleus accumbens and vulnerability to cocaine. Microdialysis revealed that basal DA release and DA extraction fraction (Ed), an indirect measure of DA uptake, are enhanced in KOR-1 knock-out mice. Analysis of DA uptake revealed a decreased Km but unchanged Vmax in knock-outs. Knock-out mice exhibited an augmented locomotor response to cocaine, which did not differ from that of wild-types administered a behavioral sensitizing cocaine treatment. The ability of cocaine to increase DA was enhanced in knock-outs, whereas c-fos induction was decreased. Although repeated cocaine administration to wild types produced behavioral sensitization, knock-outs exhibited no additional enhancement of behavior. Administration of the long-acting KOR antagonist nor-binaltorphimine to wild-type mice increased DA dynamics. However, the effects varied with the duration of KOR-1 blockade. Basal DA release was increased whereas Ed was unaltered after 1 h blockade. After 24 h, release and Ed were increased. The behavioral and neurochemical effects of cocaine were enhanced at both time points. These data demonstrate the existence of an endogenous KOR-1 system that tonically inhibits mesoaccumbal DA neurotransmission. Its loss induces neuroadaptations characteristic of "cocaine-sensitized" animals, indicating a critical role of KOR-1 in attenuating responsiveness to cocaine. The increased DA uptake after pharmacological inactivation or gene deletion highlights the plasticity of mesoaccumbal DA neurons and suggests that loss of KOR-1 and the resultant disinhibition of DA neurons trigger short- and long-term DA transporter adaptations that maintain normal DA levels, despite enhanced release.

Subsarcolemmal mitochondria isolated with the proteolytic enzyme nagarse exhibit greater protein specific activities and functional coupling.

Skeletal muscle mitochondria are arranged as a reticulum. Insight into the functional characteristics of such structure is achieved by viewing the network as consisting of "subsarcolemmal" (SS) and "intermyofibrillar" (IMF) regions. During the decades, most, but not all, published studies have reported higher (sometimes over 2-fold) enzyme and enzyme-pathway protein-specific activities in IMF compared to SS mitochondria. We tested the hypothesis that non-mitochondrial protein contamination might account for much of the apparently lower specific activities of isolated SS mitochondria. Mouse gastrocnemii (n = 6) were suspended in isolation medium, minced, and homogenized according to procedures typically used to isolate SS mitochondria. However, the supernatant fraction, collected after the first slow-speed (800×g) centrifugation, was divided equally: one sample was exposed to nagarse (MITO+), while the other was not (MITO-). Nagarse treatment reduced total protein yield by 25%, while it increased protein-specific respiration rates (nmol O2 min-1 mg-1), by 38% under "resting" (state 4) and by 84% under maximal (state 3) conditions. Nagarse therefore increased the respiratory control ratio (state 3/state 4) by 30%. In addition, the ADP/O ratio was increased by 9% and the activity of citrate synthase (U/mg) was 49% higher. Mass spectrometry analysis indicated that the MITO+ preparation contained less contamination from non-mitochondrial proteins. We conclude that nagarse treatment of SS mitochondria removes not only non-mitochondrial proteins but also the protein of damaged mitochondria, improves indices of functional integrity, and the resulting protein-specific activities.

Mice Expressing a "Hyper-Sensitive" Form of the Cannabinoid Receptor 1 (CB1) Are Neither Obese Nor Diabetic.

Multiple lines of evidence implicate the endocannabinoid signaling system in the modulation of metabolic disease. Genetic or pharmacological inactivation of CB1 in rodents leads to reduced body weight, resistance to diet-induced obesity, decreased intake of highly palatable food, and increased energy expenditure. Cannabinoid agonists stimulate feeding in rodents and increased levels of endocannabinoids can disrupt lipid metabolism. Therefore, the hypothesis that sustained endocannabinoid signaling can lead to obesity and diabetes was examined in this study using S426A/S430A mutant mice expressing a desensitization-resistant CB1 receptor. These mice display exaggerated and prolonged responses to acute administration of phytocannabinoids, synthetic cannabinoids, and endocannabinoids. As a consequence these mice represent a novel model for determining the effect of enhanced endocannabinoid signaling on metabolic disease. S426A/S430A mutants consumed equivalent amounts of both high fat (45%) and low fat (10%) chow control diet compared to wild-type littermate controls. S426A/S430A mutants and wild-type mice fed either high or low fat control diet displayed similar fasting blood glucose levels and normal glucose clearance following a 2 g/kg glucose challenge. Furthermore, S426A/S430A mutants and wild-type mice consumed similar amounts of chow following an overnight fast. While both THC and JZL195 significantly increased food intake two hours after injection, this increase was similar between the S426A/S430A mutant and wildtype control mice Our results indicate that S426A/S430A mutant mice expressing the desensitization-resistant form of CB1 do not exhibit differences in body weight, food intake, glucose homeostasis, or re-feeding following a fast.

Neuropathic pain activates the endogenous kappa opioid system in mouse spinal cord and induces opioid receptor tolerance.

Release of endogenous dynorphin opioids within the spinal cord after partial sciatic nerve ligation (pSNL) is known to contribute to the neuropathic pain processes. Using a phosphoselective antibody [kappa opioid receptor (KOR-P)] able to detect the serine 369 phosphorylated form of the KOR, we determined possible sites of dynorphin action within the spinal cord after pSNL. KOR-P immunoreactivity (IR) was markedly increased in the L4-L5 spinal dorsal horn of wild-type C57BL/6 mice (7-21 d) after lesion, but not in mice pretreated with the KOR antagonist nor-binaltorphimine (norBNI). In addition, knock-out mice lacking prodynorphin, KOR, or G-protein receptor kinase 3 (GRK3) did not show significant increases in KOR-P IR after pSNL. KOR-P IR was colocalized in both GABAergic neurons and GFAP-positive astrocytes in both ipsilateral and contralateral spinal dorsal horn. Consistent with sustained opioid release, KOR knock-out mice developed significantly increased tactile allodynia and thermal hyperalgesia in both the early (first week) and late (third week) interval after lesion. Similarly, mice pretreated with norBNI showed enhanced hyperalgesia and allodynia during the 3 weeks after pSNL. Because sustained activation of opioid receptors might induce tolerance, we measured the antinociceptive effect of the kappa agonist U50,488 using radiant heat applied to the ipsilateral hindpaw, and we found that agonist potency was significantly decreased 7 d after pSNL. In contrast, neither prodynorphin nor GRK3 knock-out mice showed U50,488 tolerance after pSNL. These findings suggest that pSNL induced a sustained release of endogenous prodynorphin-derived opioid peptides that activated an anti-nociceptive KOR system in mouse spinal cord. Thus, endogenous dynorphin had both pronociceptive and antinociceptive actions after nerve injury and induced GRK3-mediated opioid tolerance.

Targeted disruption of G0/G1 switch gene 2 enhances adipose lipolysis, alters hepatic energy balance, and alleviates high-fat diet-induced liver steatosis.

Recent biochemical and cell-based studies identified G0/G1 switch gene 2 (G0S2) as an inhibitor of adipose triglyceride lipase (ATGL), a key mediator of intracellular triacylglycerol (TG) mobilization. Here, we show that upon fasting, G0S2 protein expression exhibits an increase in liver and a decrease in adipose tissue. Global knockout of G0S2 in mice enhanced adipose lipolysis and attenuated gain of body weight and adiposity. More strikingly, G0S2 knockout mice displayed a drastic decrease in hepatic TG content and were resistant to high-fat diet (HFD)-induced liver steatosis, both of which were reproduced by liver-specific G0S2 knockdown. Mice with hepatic G0S2 knockdown also showed increased ketogenesis, accelerated gluconeogenesis, and decelerated glycogenolysis. Conversely, overexpression of G0S2 inhibited fatty acid oxidation in mouse primary hepatocytes and caused sustained steatosis in liver accompanied by deficient TG clearance during the fasting-refeeding transition. In response to HFD, there was a profound increase in hepatic G0S2 expression in the fed state. Global and hepatic ablation of G0S2 both led to improved insulin sensitivity in HFD-fed mice. Our findings implicate a physiological role for G0S2 in the control of adaptive energy response to fasting and as a contributor to obesity-associated liver steatosis.

Long-term consequences of perinatal fatty acid amino hydrolase inhibition.

BACKGROUND AND PURPOSE: Fatty acid amide hydrolase inhibitors show promise as a treatment for anxiety, depression and pain. Here we investigated whether perinatal exposure to URB597, a fatty acid amide hydrolase inhibitor, alters brain development and affects behaviour in adult mice. EXPERIMENTAL APPROACH: Mouse dams were treated daily from gestational day 10.5 to 16.5 with 1, 3 or 10 mg kg−1 URB597. MS was used to measure a panel of endocannabinoids and related lipid compounds and brain development was assessed at embryonic day 16.5. Separate cohorts of mouse dams were treated with 10 mg kg−1 URB597, from gestational day 10.5 to postnatal day 7, and the adult offspring were assessed with a battery of behavioural tests. KEY RESULTS: Perinatal URB597 exposure elevated anandamide and related N-acyl amides. URB597 did not induce signs of toxicity or affect dam weight gain, neurogenesis or axonal development at embryonic day 16.5. It did lead to subtle behavioural deficits in adult offspring, manifested by reduced cocaine-conditioned preference, increased depressive behaviours and impaired working memory. Anxiety levels, motor function and sensory-motor gating were not significantly altered. CONCLUSIONS AND IMPLICATIONS: Taken together, the present results highlight how exposure to elevated levels of anandamide and related N-acyl amides during brain development can lead to subtle alterations in behaviour in adulthood. LINKED ARTICLES: This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6

CNS opioid signaling separates cannabinoid receptor 1-mediated effects on body weight and mood-related behavior in mice.

Existing monotherapies for the treatment of obesity provide only modest weight loss and/or have adverse side effects, and this is also the case with the cannabinoid receptor 1 (CB1) inverse agonist, rimonabant. We aimed to investigate the possibility of improving efficacy and reducing side effects of rimonabant by cotreatment with opioid system antagonists. Using both genetic and pharmacological removal of opioid signaling in mice, we investigated changes in body weight, food intake, and fat mass as well as behavioral outcomes of interactions between opioid ligands and the CB1 using the inverse agonist, rimonabant. The ability of rimonabant to reduce weight is enhanced by removal of with µ-opioid receptor signaling, while not being greatly affected by κ-opioid receptor blockade. Additionally, lack of opioid signaling, especially κ-opioid receptor, attenuated the ability of rimonabant to decrease immobility time in the Porsolt forced-swim test, a preclinical model of depression. These results indicate that the endogenous opioid system is involved in modulating both the metabolic and mood effects of rimonabant.